How Might an Ecologist Test Whether a Species Is Occupying

How might an ecologist test whether a species is occupying all of its fundamental niche or only a portion of it?

A) Study the temperature range and humidity requirements of the species.
B) Observe if the niche size changes after the addition of nutritional resources to the habitat.
C) Observe if the niche size changes after the introduction of a similar non-native species.
D) Measure the change in reproductive success when the species is subjected to environmental stress.
E) Observe if the species expands its range after the removal of a competitor.